Search results for "cfd"

Numerical prediction of flow fields in baffled stirred vessels: A comparison of alternative modelling approaches

1998

Abstract Numerical simulations of the flow field in baffled mixing tanks, based on three alternative methods, are presented and discussed. In the first method, the impeller is not explicitly simulated, and its effects are modelled by imposing suitable, empirically derived, boundary conditions to the external flow. In the second method, the whole vessel volume is divided into two concentric, partially overlapping, regions. In the inner region, containing the impeller, the flow field is simulated in the rotating reference frame of the latter, while in the outer region simulations are conducted in the reference frame of the laboratory. Information is iteratively exchanged between the two regio…

Dense solid–liquid off-bottom suspension dynamics: Simulation and experiment

2009

Dense solid–liquid off-bottom suspension inside a baffled mechanically stirred tank equipped with a standard Rushton turbine is investigated. Dynamic evolution of the suspension from start-up to steady-state conditions has been determined by both visual experiments and computational fluid dynamics (CFDs). A classical Eulerian–Eulerian multifluid model (MFM) along with the “homogeneous” k–ε turbulence model is adopted to simulate suspension dynamics. In these systems the drag inter-phase force affects both solids suspension and distribution. Therefore, different computational approaches are tested in order to compute this term. Simulation results are compared with images obtained from the re…

CFD analysis of concentration polarization phenomena in spacer-filled channels for Reverse Electro-Dialysis

2012

In this work, carried out within the EU-FP7 funded REAPower project, CFD simulations were carried out in order to study the fluid flow behaviour and mass transport phenomena within spacer-filled channels.

CFD PREDICTION OF BUBBLES BEHAVIOUR IN 2-DIMENSIONAL GAS-SOLID FLUIDIZED BEDS

2008

In recent years the use of Computational Fluid Dynamics (CFD) is significantly increasing to simulate multi-phase flows. It is invariably emphasized that a necessary step towards the development of reliable fully predictive CFD models is an extensive experimental validation of the simulation results. This work in particular focuses on the CFD simulation of a lab-scale 2D fluidized bed and the relevant experiments, in order to validate the prediction capability of the used codes and models. It must be emphasized that both experimental and computational quantitative data have been obtained by means of an original Digital Image Analysis Technique, that allows coherent comparison of computation…

Pressure drop at low reynolds numbers in woven-spacer-filled channels for membrane processes: CFD prediction and experimental validation

2017

The energy consumption due to pumping power is a crucial issue in membrane processes. Spacers provide mechanical stability and promote mixing, yet increasing pressure drop. Woven spacers and their behaviour at low Reynolds numbers are less studied in the literature. Nevertheless, they are typical of some membrane technologies, as reverse electrodialysis (RED). RED is a promising technology for electric power generation by the chemical potential difference of two salt solutions within a stack equipped by selective ion-exchange membranes. The mechanical energy required for pumping the feed solutions, can dramatically reduce the net power output. In this work computational fluid dynamics (CFD)…

Modelling Turbulent Inter-Phase Drag in Mechanically Stirred Solid-Liquid Suspensions

2012

CFD Simulation of Particle Suspension Height in Stirred Vessels

2004

Computational fluid dynamics (CFD) simulation capabilities for stirred solid–liquid dense systems are explored. These systems may give rise to the formation of a thick and well defined clear liquid layer in the upper part of the vessel, whose extension progressively reduces with increasing impeller speed. Experimental measurements of the suspension height (the height of the particle laden layer) were carried out at various agitation speeds for a variety of solid–liquid systems in a fully baffled transparent tank. A clear layer of liquid was actually observed in all runs, with the suspension height almost linearly dependent on agitation speed. CFD simulations of the above described systems w…

Application of computational fluid dynamics technique in membrane distillation processes

2022

This Chapter illustrates the application of CFD to spacer-filled channels for membrane distillation. The topics discussed cover finite volume grids and grid independence, the unit-cell treatment of spatially periodic net spacers, and the dependence of flow and thermal fields and overall performance parameters (pressure drop and mean heat transfer coefficients) upon geometry and operating conditions (Reynolds number, flow attack angle, pitch-to-height ratio, spacer thermal conductivity, thermal boundary conditions, and one-side vs. two-side heat transfer).

SIMULAZIONI CFD DEL CAMPO DI MOTO A BASSO NUMERO DI REYNOLDS IN BIOREATTORI AGITATI CON E SENZA SETTI FRANGIVORTICE

2016

I recipienti meccanicamente agitati sono apparecchiature frequenti dell’industria chimica di processo. Questi sono tipicamente dotati di setti frangivortice (recipienti baffled) atti a rompere il moto prettamente tangenziale tipico dei recipienti sprovvisti di setti (recipienti unbaffled) e convertirlo in moto assiale e radiale. La presenza dei setti evita inoltre nella zona centrale del sistema la formazione del vortice d’aria che può talvolta essere indesiderato o in taluni casi creare instabilità una volta arrivato alla girante. I recipienti unbaffled sono considerati quindi dei miscelatori meno efficienti rispetto a quelli provvisti di setti. Tali sistemi sono pertanto ad oggi impiegati…

Geometrical characterization of reverse electrodialysis stack via CFD simulations

2012

In the presente work, CFD simulations were carried out in order to assess the effects of different parameters on the global process efficiency, such as the choice of spacer material and morphology, and the optimisation of feed and blowdown distribution systems